LCDs are being used in more and more different applications. One trend is that LCDs are becoming bigger in size to suit certain new uses. This means such kind of LCD has a larger viewing area and high definition. LCDs employing thin film transistors (TFTs) are called TFT-LCDs. Generally, TFT-LCDs are prone to have a problem of gate delay due to the elongated gate lines therein, and an associated problem of gate delay phenomenon of scanning signals transmitted therein. Gate delay usually results in image flickering or other display problems.
Referring to FIG. 4, a typical LCD 100 includes a gate driving circuit 110, a data driving circuit 120, and a liquid crystal panel 130. The gate driving circuit 110 is configured for providing a plurality of scanning signals to the liquid crystal panel 130, and the data driving circuit 120 is configured for providing a plurality of gray scale voltages to the liquid crystal panel 130.
The liquid crystal panel 130 includes a plurality gate lines 101 which are parallel to each other, a plurality of data lines 102 which are parallel to each other and which intersect the gate lines 101, a plurality of TFTs 103 arranged at crossings of the gate lines 101 and the data lines 102, a plurality of pixel electrodes 104, and a plurality of common electrodes 105 generally opposite to the pixel electrodes 104. Each of areas bounded by two adjacent gate lines 101 and two adjacent data lines 102 is defined as a pixel area. The gate driving circuit 110 sequentially outputs a plurality of scanning signals to the gate lines 101. The data driving circuit 120 applies a plurality of gray scale voltages to source electrodes 1032 (see FIG. 5) of corresponding TFTs 103 when a corresponding gate line 101 is scanned.
Referring also to FIG. 5, an equivalent circuit diagram of a pixel area is shown. A gate electrode 1031 of the TFT 103 is connected to the corresponding gate line 101, the source electrode 1032 of the TFT 103 is connected to the corresponding data line 102, and a drain electrode 1033 of the TFT 103 is connected to the corresponding pixel electrode 104. Because the gate line 101 has a certain inherent resistance R, and a parasitic capacitance Cgd is generated between the gate electrode 1031 and the drain electrode 1033, a resistance-capacitance (RC) delay circuit is formed at the pixel area. In one gate line 101, therefore, many such RC delay circuits are connected in series. The RC delay circuits can delay the scanning signals applied to the gate line 101, and thus the waveform of the scanning signal can be distorted.
Referring also to FIG. 6, this shows scanning signal waveforms provided at two ends of one of the gate lines 101. One end is adjacent to the gate driving circuit 110, and the other end is far from the gate driving circuit 110. “Vg1” is the waveform of the scanning signal at the end of the gate line 101 that is adjacent to the gate driving circuit 110, and “Vg2” is the waveform of the scanning signal at the end of the gate line 101 that is far from the gate driving circuit 110. That is, the waveform “Vg2” is a distorted waveform of the scanning signal, due to delaying by the serial RC delay circuits. “Von” denotes a turn-on voltage of the TFTs 103 along the gate line 101, and “Voff” denotes a turn-off voltage of the TFTs 103 along the gate line 101. Because of the distortion of the waveform of the scanning signal, the turning on of a TFT 103 at the end of the gate line 101 far away from the gate driving circuit 110 is delayed. For example, the delay may be a time period “t” seconds, as shown in FIG. 3. That is, an on-state period of TFTs 103 far from the gate driving circuit 110 is shorter than it should be.
Because a gray scale voltage will not be applied to the drain electrode until the corresponding TFT 103 is turned on, the TFT 103 which is far from the gate driving circuit 110 is not properly charged with the gray scale voltage. Thus, the image display is deteriorated in the corresponding pixel area. Typically, many pixel areas are affected because the corresponding TFTs 103 lack proper charging of gray scale voltages. In this case, the image of the LCD 100 has flickers.
What is needed, therefore, is a liquid crystal display which can overcome the above-described deficiencies.